1. Field of the Invention
The invention relates to a liquid crystal compound, a liquid crystal composition, and a liquid crystal display device. The invention relates more specifically to a fluorobenzene derivative having fluorine at a lateral position, which is a liquid crystal compound, a liquid crystal composition with a nematic phase comprising this compound, and a liquid crystal display device comprising this composition.
2. Description of Related Art
A liquid crystal display device typified by a liquid crystal display panel, a liquid crystal display module and so forth utilizes optical anisotropy, dielectric anisotropy and so forth which are possessed by a liquid crystal compound (in this invention a liquid crystal compound means a generic term for a compound having a nematic phase, a smectic phase and so forth, and a compound having no liquid crystal phases but useful as a component of a liquid crystal composition.). As operating modes of this liquid crystal display device, a variety of modes are known, such as PC (phase change), TN (twisted nematic), STN (super twisted nematic), BTN (bistable twisted nematic), ECB (electrically controlled birefringence), OCB (optically compensated bend), IPS (in-plane switching) and VA (vertical alignment) modes.
It is known that among these operating modes, the ECB mode, the IPS mode, the VA mode and so forth are utilizing a homeotropic property of liquid crystal molecules, and that a limited-viewing angle which is a disadvantage of conventional display modes such as the TN and STN modes can be improved especially by use of the IPS and VA modes.
A large number of liquid crystal compounds in which hydrogen on the benzene-ring is replaced by fluorine have been examined conventionally as components for a liquid crystal composition having negative dielectric anisotropy which is useable to the liquid crystal display device with these operating modes (for example, refer to the patent documents Nos. 1 to 4.).
For example, the compounds (A) and (B) in which hydrogen on the benzene ring is replaced by fluorine have been described (refer to the patent documents Nos. 1 and 2). However, such compounds do not have a large negative dielectric anisotropy.
The terphenyl compounds (C) having fluorine at a lateral position is described (refer to the patent document No. 3). However, this compound has a high melting point and a poor compatibility.
The compound (D) having an ester bonding group and a lateral fluorine is described (refer to the patent document No. 4). However, the compound (D) does not have a large negative dielectric anisotropy.

The patent documents cited herein are No. 1: JP H02-503441 A (1990); No. 2: WO 1989/02425 A; No. 3: JP H11-116512 A (1999); and No. 4: WO 1989/06678 A.